U.S. patent number 6,071,597 [Application Number 08/919,883] was granted by the patent office on 2000-06-06 for flexible circuits and carriers and process for manufacture.
This patent grant is currently assigned to 3M Innovative Properties Company. Invention is credited to Moses M. David, Justine A. Mooney, Thach G. Truong, Rui Yang.
United States Patent |
6,071,597 |
Yang , et al. |
June 6, 2000 |
**Please see images for:
( Certificate of Correction ) ** |
Flexible circuits and carriers and process for manufacture
Abstract
A flexible circuit carrier including at least one layer of
polymer dielectric material, at least one layer of conductive
material thereover, each layer having two major surfaces, at least
one of said layers having at least one aperture therein, wherein at
least one layer has a material coated on at least a portion thereof
having a Young's Modulus of from about 100 to about 200 GPa, a
dielectric constant (between 45 MHz and 20 GHz) of from about 8 to
about 12, and a Vickers hardness of from about 2000 to about 9000
kg/mm.sup.2.
Inventors: |
Yang; Rui (Austin, TX),
Truong; Thach G. (Columbia, MO), Mooney; Justine A.
(Austin, TX), David; Moses M. (Woodbury, MN) |
Assignee: |
3M Innovative Properties
Company (St. Paul, MN)
|
Family
ID: |
25442802 |
Appl.
No.: |
08/919,883 |
Filed: |
August 28, 1997 |
Current U.S.
Class: |
428/209; 174/254;
428/408; 428/458; 174/258; 257/E23.177; 257/E23.065 |
Current CPC
Class: |
H01L
23/4985 (20130101); H01L 23/5387 (20130101); H05K
3/28 (20130101); H05K 3/388 (20130101); Y10T
428/30 (20150115); Y10T 428/31681 (20150401); H01L
2924/0002 (20130101); H05K 2201/0323 (20130101); H05K
2201/0179 (20130101); Y10T 428/24917 (20150115); H05K
1/0393 (20130101); H01L 2924/3011 (20130101); H01L
2924/0002 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
H01L
23/48 (20060101); H01L 23/538 (20060101); H01L
23/52 (20060101); H01L 23/498 (20060101); H05K
3/38 (20060101); H05K 3/28 (20060101); H05K
1/00 (20060101); B32B 009/00 () |
Field of
Search: |
;257/646,758,774
;174/254,258 ;428/408,458,477.4,209 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
0064343A2 |
|
Jul 1995 |
|
EP |
|
02046526 |
|
Feb 1990 |
|
JP |
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2-223451 |
|
Sep 1990 |
|
JP |
|
07118853 |
|
May 1995 |
|
JP |
|
2287473 |
|
Sep 1995 |
|
GB |
|
Other References
"Plasma deposition of hydrogenated amorphous carbon; growth rates,
properties & structures", N.Fourches & G. Turban, Thin
Solid Films, 240 (1994), pp. 28-38. .
"Effect of diluent gases added during deposition on the etching
characteristics of diamond-like carbon films", J.Seth, R.Padiyath
& S.Babu, Thin Solid Films, 212 (1994), pp. 251-255. .
"Compilation of Diamond-Like Carbon Properties for Barriers and
Hard Coatings", D.Outka et al, Sandia Nat'l Labs. Rel. #SAND94-8219
(1994). .
"Structure and Electronic Properties of Diamond-Like Carbon",
J.Robertson, Diamond and Diamond-Like Carbon Films, NATO Advanced
Study Institute, Pisa (1990)..
|
Primary Examiner: Lam; Cathy
Attorney, Agent or Firm: Fonseca; Darla P.
Claims
What is claimed is:
1. A flexible printed circuit comprising:
a) at least one layer of polymer dielectric material,
b) at least one layer of electrically conductive material
thereover, and
c) at least one circuit trace,
each of said dielectric layers and each of said conductive layers
having two major surfaces, at least one layer selected from a
dielectric layer or a conductive layer having at least one aperture
therein,
wherein at least one of said dielectric layers has a material
selected from the group consisting of diamond-like carbon,
hydrogenated diamond-like carbon, functionalized diamond-like
carbon, silicone nitride, boron nitride, silicon carbide, silicon
dioxide and boron trifluoride coated on at least a portion of at
least one major surface of said dielectric layers, said material
having a Young's Modulus of from about 100 to about 200 GPa, a
dielectric constant between 45 MHz and 20 GHz of from about 8 to
about 12, and a Vickers hardness of from about 2000 to about 9000
kg/mm.sup.2.
2. A flexible circuit according to claim 1 wherein said material
has a thickness of between about 500 Angstroms to about 3000
Angstroms.
3. A flexible circuit according to claim 1 wherein said material is
selected from diamond-like carbon and hydrogenated diamond-like
carbon.
4. A flexible circuit according to claim 1 wherein said layer of
material is a covercoat deposited as an uppermost layer.
5. A flexible circuit according to claim 1, comprising:
a) a polymeric dielectric material having two major surfaces,
b) a layer of diamond-like carbon on at least a portion of at least
one major surface of said dielectric material,
c) a first layer of metal atop said layer of diamond-like carbon
layer, and
d) a second layer of metal electroplated onto said first layer.
6. A flexible circuit according to claim 5 wherein said layer of
material is deposited as an uppermost covercoat layer.
7. A flexible circuit according to claim 1 comprising:
a) a polymeric dielectric material having two major surfaces,
b) a layer of non-metallic material on at least a portion of at
least one major surface of said dielectric material, said
non-metallic material having a Vickers hardness greater than 2000
and a dielectric constant between 45 MHz and 20 GHz greater than
8,
a first layer of metal on said non-metallic layer, and
a second layer of metal electroplated onto said first layer.
8. A flexible circuit comprising
a) at least one layer of polymer dielectric material,
b) at least one layer of electrically conductive material
thereover, and
c) at least one circuit trace,
each of said dielectric layers and each of said conductive layers
having two major surfaces, at least one layer selected from a
dielectric layer or a conductive layer having at least one aperture
therein,
wherein at least one of said dielectric layers has a material
coated on at least a portion of at least one major surface of said
dielectric layers, said material having a Young's Modulus of from
about 100 to about 200 GPa, a dielectric constant between 45 MHz
and 20 GHz of from about 8 to about 12, and a Vickers hardness of
from about 2000 to about 9000 kg/mm.sup.2,
wherein said material is diamond-like carbon wherein said
diamond-like carbon has a functionalized surface.
9. A flexible circuit according to claim 8 wherein said surface of
said diamond-like carbon is functionalized with an element selected
from the group consisting of silicon, oxygen, nitrogen, sulfur,
titanium, chromium, copper, fluorine and nickel.
10. A flexible circuit according to claim 8 wherein said
functionalized diamond-like carbon is functionalized hydrogenated
diamond-like carbon.
11. A flexible circuit comprising:
a) at least one layer of polymer dielectric material,
b) at least one layer of electrically conductive material
thereover,
said polymer dielectric layer and said electrically conductive
layer having two major surfaces, said polymer dielectric layer
having a circuit trace, and at least one feature selected from an
aperture, a stiffener, and a groundplane, said feature having a at
least a portion thereof coated diamond-like carbon with a material
having a Young's Modulus of from about 100 to about 200 GPa, a
dielectric constant between 45 MHz and 20 GHz of from about 8 to
about 12, and a Vickers hardness of from about 2000 to about 9000
kg/mm.sup.2.
12. A flexible circuit according to claim 11 wherein said feature
is a blind via, said blind via having an interior and a base, at
least one of which is coated with said diamond-like carbon
material.
13. A flexible circuit according to claim 11 wherein said
diamond-like
carbon material is hydrogenated diamond-like carbon.
14. A flexible circuit according to claim 11 further comprising at
least one additional layer of dielectric material.
Description
FIELD OF THE INVENTION
The invention relates to flexible circuits and carriers for
flexible circuits made therefrom which are coated, either
selectively or continuously, with at least one layer of
diamond-like carbon or similar material, and a process for
producing flex circuits having diamond-like carbon layers. More
specifically, the invention relates to amorphous diamond-like
carbon film and to materials having similar properties that enhance
the performance, manufacturability, reliability, versatility,
and/or assembly of flexible circuit carriers, and corresponding
flexible circuits made therewith.
BACKGROUND OF THE INVENTION
Flexible circuits are circuits which are formed on flexible
dielectric substrates such as polymeric materials. The circuits may
have one or more conductive layers as well as circuitry on one of
the major surfaces or on both major surfaces. The circuits often
include additional functional layers, e.g., insulative layers,
adhesive layers, encapsulating layers, stiffening layers and the
like. Flexible circuits are typically useful for electronic
packages where flexibility, weight control and the like are
important. In many high volume situations, flexible circuits also
provide cost advantages associated with efficiency of the
manufacturing processes employed.
U.S. Pat. No. 4,914,551 discloses circuits as provided on flexible
dielectric materials. U.S. Pat. No. 4,231,154 discloses a flexible
circuit with conductive traces on one or more layers. U.S. Pat. No.
4,480,288 discloses flexible circuits with circuitry on both major
surfaces. U.S. Pat. No. 5,401,913 discloses a multi-layer flexible
circuit consisting of multiple flexible circuits stacked relative
to one another and interconnected using metallized through-holes
commonly referred to as vias. All of these references disclose
various aspects of flexible circuits, but none make mention of the
benefits of utilizing diamond-like carbon or materials providing
diamond-like carbon properties to enhance the performance and
functionality of flex circuits. All of these referenced patents are
hereby incorporated by reference.
Various types of flexible circuits are known in the industry.
Generally speaking, the key differences in the various circuits
stem from a number of design requirements for the devices that the
circuit is connecting together along with the requirements and
limitations of the processing methods used to make the circuit.
Typically, the flexible circuit is connecting a semi-conductor of
some sort (integrated circuit, microprocessors, or the like) to
another flex circuit, a rigid circuit board or a component of a
device. The design factors associated with items the circuit is
connecting include, but are not limited to, the number of input and
output (I/O) leads from a semi-conductor that needs to be
connected, the means and process for interconnection of the
flexible circuits to another circuit or to a device, the required
size and weight of the finished product, the environmental
conditions under which the circuit will be assembled and used, and
the data transmission rates to which the circuit will be subjected.
All of these design factors as well as the methods and equipment
used to manufacture the circuit will at least partially determine
circuit design parameters such as whether the means for
interconnecting the flexible circuit to another item is a Ball Grid
Array (BGA), array of bonding pads, or series of discrete leads;
whether the circuit has one or more conductive layers, and if so,
on one or both sides; if the materials need to be chemically stable
to prevent outgassing; or if they need to be compatible for use and
assembly at elevated temperature and humidity levels.
Diamond coatings, diamond-like carbon films, and uses for them are
also known. These coatings and films possess a number of desirable
properties, including high hardness, optical clarity, low friction,
high thermal conductivity, high dielectric constant, high chemical
stability, low gas and vapor permeability, and other properties.
Furthermore, the composition of diamond-like carbon can be modified
to control the measured value for many of these properties. The
typical properties for diamond-like carbon are presented in the
table below.
______________________________________ Typical Properties for
Diamond-Like Carbon ______________________________________ Density,
g/cm.sup.3 1.6-3.0 Hardness, Vickers, kg/mm.sup.2 2000-9000 Young's
Modulus, Gpa 100-200 Dielectric Constant 8-12 (between 45 MHz and
20 GHz) Electrical Resistivity, ohms/cm 10.sup.5 -10.sup.15
Excitation Coefficient .001-0.5 (between 200 and 1000 nm) Index of
Refraction @ 10 .mu.m 1.8-2.4 Optical Band-Gap 0.8-3.0 eV Thermal
Conductivity @ 25 C., 400-1000 W/m-K
______________________________________
Diamond-like carbon coatings and films may be formed and deposited
by processes using hydrocarbon or carbon sources. Carbon source
deposition methods include ion beam sputter deposition, laser
ablation deposition, ion beam assisted carbon evaporation.
Hydrocarbon source deposition methods include ion beam, microwave
plasma, and directed plasma discharge, various types of
plasma-assisted chemical deposition methods, radio frequency plasma
deposition, cathodic arc deposition, and the like. U.S. Pat. Nos.
4,698,256; 4,400,410; 4,383,728; 4,504,410; and 4,746,538 disclose
processes for producing diamond-like carbon films and coatings, all
of which are incorporated herein by reference.
Diamond and diamond-like carbon films are currently being used in a
variety of applications. These applications include eyeglasses,
semiconductors, drilling and machining tools, beverage containers,
and many other applications requiring the properties afforded by
diamond-like carbon. U.S. Pat. No. 5,508,071 discloses an annular
interior surface having a layer of diamond coating for improve
abrasion resistance. The coating is deposited on substrates such as
metal, alloys, and ceramics. Because chemical vapor deposition
(CVD) of diamond layers takes place at very high temperatures, it
cannot be used for many polymeric substrates such as polyimide
which will degrade at the elevated diamond-forming temperatures.
Further, the polycrystalline nature of CVD diamond dictates a very
hard, brittle coating with little flexibility.
The term "diamond-like carbon" is typically applied to
noncrystalline materials, especially those in which tetrahedral
diamond bonds predominate. U.S. Pat. No. 4,576,964 discloses
barrier films made from flexible polymeric substrates having
amorphous carbon coatings adhering thereto. U.S. Pat. No. 5,508,092
discloses optically transparent abrasion wear resistant coated
substrates comprising a parent substrate, one or more interlayers
and a top coating of diamond-like carbon or other low-friction
material. U.S. Pat. No. 5,559,367 discloses the use of diamond-like
carbon to electrically insulate levels within semiconductors. U.S.
Pat. No. 4,809,876 discloses polymeric beverage containers
utilizing a coating of diamond-like carbon to reduce the gas and
vapor permeability through the container.
The current inventors have now discovered that one or more
conformal coatings of diamond-like carbon deposited onto a carrier
for a flexible circuit or a tab tape construction during the
appropriate steps of the manufacturing process results in an
improved construction exhibiting a number of desirable physical and
functional attributes not otherwise possible with existing flex
circuit constructions or materials. These attributes contribute to
improvements in the areas of manufacturability, performance, cost,
reliability, and versatility of the flex circuit. Although
diamond-like carbon is the preferred material to provide the
desired improvements and enhancements, other materials having the
properties comparable to diamond-like carbon could also be
used.
SUMMARY OF THE INVENTION
In the broadest aspect, this invention provides a carrier for a
flexible circuit comprising at least one feature having at least
one conformal layer of a coating deposited thereon, said material
having a Young's Modulus of from about 100 to about 200 GPa, a
dielectric constant between 45 MHz and 20 GHz of from about 8 to
about 12, and a Vickers hardness of from about 2000 to about 9000
kg/mm.sup.2.
The invention also provides flexible circuits comprising such
carrier and electrical traces. The circuitry may be formed by any
conventional processes, and of any conventional materials.
Preferred carriers for flexible circuits of the invention are those
having at least one conformal layer of diamond-like carbon
deposited on at least a portion of one surface or feature
thereof.
In one embodiment, a conformal layer of diamond-like carbon is
deposited as a covercoat over one entire layer of the carrier or
flexible circuit; in another embodiment a layer is deposited only
on selected areas, such as around vias or through-holes. A
conformal coating of diamond-like carbon may also be deposited on
features other than surfaces such as the interior walls of such
vias or through-holes. In yet another embodiment, layers of
diamond-like carbon are deposited on a plurality of layers as the
circuit structure is built.
In one embodiment, polymeric flexible circuits and carriers of the
invention are formed from a flexible dielectric material, and
include a first intermediate layer coated thereon, and a conformal
diamond-like carbon second intermediate layer coated thereon, and
an electrically conductive layer coated thereon.
In another embodiment, an overcoated flex circuit is useful for
environmentally sensitive applications and/or applications where a
mask for a least a portion of the circuit is needed. A conformal
layer of diamond-like carbon coated over the flex circuit insulates
the conductive traces, and eliminates the potential for
contamination from outgassing. The invention also provides a
process for making a flexible circuit carrier wherein features to
be subjected to laser drilling or ablation are strengthened by the
layer of diamond-like carbon, allowing for improved features to be
created. Such features have better planarity and surface
characteristics than those features formed without the conformal
layer of material.
The following terms have the defined meanings when used herein.
1. The terms "carrier" and "flexible circuit carrier" mean a
package useful for a flexible circuit, but which does not yet have
circuit traces formed thereon.
2. The term "aperture" refers to an opening in a layer of the
flexible circuit carrier. The aperture may extend through a portion
of the layer, or may extend completely through the layer. Apertures
may be formed by a variety of techniques including mechanical
punching, chemical milling, and laser ablation.
3. The term "through hole" refers to an aperture which extends
completely through a layer of the flexible circuit carrier exposing
a metal trace on one side.
4. The term "via" refers to a metallized through hole that connects
a conductive trace to another conductive trace or plane.
5. The term "blind via" refers to a metallized aperture which does
not extend completely through a layer of the flexible circuit
carrier.
6. The terms "diamond-like carbon" and "carbon rich film" are
synonymous and interchangeable in the industry, and refer to carbon
films primarily consisting of carbon without long range atomic
order as disclosed in Plasma Deposited Films, Ed. J. Mort and F.
Joanne, CRC Press, Boca Raton, Fla., 1986.
7. The terms "tape automated bonding" and "TAB" are synonymous and
refer to the format and assembly method of the circuit.
8. The terms "etching" and "milling" are used synonymously, and
include mechanical, chemical and optical processes for removing
material, including chemical etching, laser ablation, mechanical
milling and the like.
9. The term "feature" means any subpart of a flexible circuit
carrier, including such items as polymeric layers, metal layers,
and surfaces of such layers, solder balls, traces, stiffeners,
ground planes, and the like, without limitation.
10. The term "doping" means surface functionalization of the
coating by introduction of another compound into the surface.
All ratios, parts, and percents described herein are by weight,
unless otherwise specifically stated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a carrier for a flexible
circuit showing a layer of diamond-like carbon deposited between
the dielectric layer and a layer of conductive material.
FIG. 2 is a cross-sectional view of a carrier for a flexible
circuit showing diamond-like carbon deposited on both sides of the
dielectric layer.
FIG. 3 is a cross-sectional view of a carrier for a flexible
circuit showing a layer of diamond-like carbon deposited between
the non-circuit side of the dielectric layer.
FIG. 4 is a cross-sectional view of a flexible circuit showing a
layer of diamond-like carbon deposited over the circuit traces.
FIG. 5 is a cross-sectional view of a carrier for a flexible
circuit showing a layer of diamond-like carbon deposited on the
circuit side of the dielectric layer and a layer of layer light
absorbing material between the layer of diamond-like carbon and the
conductive layer.
FIG. 6 is a cross-sectional view of a carrier for a flexible
circuit showing a layer of laser light absorbing material deposited
on the circuit side of the dielectric layer and a layer of
diamond-like carbon between the layer of laser light absorbing
material and the conductive layer.
FIG. 7 is a cross-sectional view of a carrier for a flexible
circuit showing a layer of laser light absorbing material deposited
on the circuit side of the dielectric layer and a layer of
diamond-like carbon deposited to the non-circuit side of the
dielectric layer.
FIG. 8 is a cross-sectional view of a flexible circuit having at
least one aperture through the dielectric layer, a layer of
diamond-like carbon deposited on the non-circuit side of the
circuit, and a layer of laser light absorbing material deposited on
the layer of diamond-like carbon.
FIG. 9 is a cross-sectional view of a flexible circuit having at
least one aperture through the dielectric layer, a layer of
diamond-like carbon deposited on the non-circuit side of the
circuit, and a layer of laser light absorbing material deposited on
the circuit side of the dielectric layer.
FIG. 10 is a first fragmentary perspective view of one embodiment
of the coating apparatus of the present invention.
FIG. 11 is a second fragmentary perspective view of the apparatus
of FIG. 10 taken from a different vantage point.
FIG. 12 is a fragmentary perspective view of another embodiment of
the coating apparatus of the present invention removed from its gas
containing chamber.
FIG. 13 is a second perspective view of the embodiment of FIG. 12
taken from a different vantage point.
DETAILED DESCRIPTION OF THE INVENTION
Flexible circuits and carriers of the invention are those having
coated on at least a portion of one feature, a conformal layer of a
material having a said material having a Young's Modulus of from
about 100 to about 200 GPa, a dielectric constant (between 45 MHz
and 20 GHz) of from about 8 to about 12, and a Vickers hardness of
from about 2000 to about 9000 kg/mm.sup.2.
The conformal layer is deposited on at least one feature of the
flexible circuit carriers and flexible circuits of the invention to
provide a variety of benefits to the flexible polymer circuit.
Layers may be deposited on features such as surface(s) of polymeric
or metal layers, vias, solder balls, stiffeners, circuit traces and
the like. Flexible circuits and carriers of the invention may have
a single conformal layer of a coating on a single feature, or
conformal coatings on multiple features. Multiple conformal layers
of the material may also be used on a single feature.
Useful materials include diamond-like carbon, silicone nitride,
boron nitride, boron, trifluoride, silicone carbide, silicone
dioxide and the like.
Preferably, such material is diamond-like carbon (DLC). Also known
as thin film carbon rich coatings, diamond-like carbon coatings
contain two types of carbon-carbon bonds; trigonal graphite bonds
(sp2) and tetrahedral diamond bonds(sp3), with tetrahedral bonds
predominating. The films thus exhibit many of the properties of
diamond, e.g., it is quite hard, chemically inert, corrosion
resistant and impervious to water vapor and oxygen, and some of the
properties of graphite, e.g., smoothness, and strong adhesion to
polymeric materials. It also has an extremely low electrical
conductivity and optical transparency over a wide range. Useful
diamond-like carbon layers for flexible circuit carriers and
flexible circuits of the invention have a thickness of from about
500 Angstroms, to about 3000 Angstroms, preferably from about 1000
Angstroms to about 2000 Angstroms.
When tested against uncoated polyimide under the same conditions, a
layer of diamond-like carbon having a thickness of 1000 Angstroms
coated onto a 50 .mu.m (2 mil) polyimide has been found to increase
the definition, concentricity and registration of laser ablated
apertures by as much as 95%; decrease the transmission rate of
water and oxygen by as much as 92% and 93%, respectively; decrease
adhesion loss between the polyimide and copper by as much as 96%;
increase the flexural stiffness by as much as 43%, and virtually
eliminate the scratching of the polyimide during processing. It has
also been found that the circuits may be selectively coated to
provide benefits in specific areas of the structure, or may be
fully coated to provide improved strength and flex to all
areas.
Depending on the application, it is desirable for the circuit or
carrier to possess enhanced mechanical, thermal, electrical,
optical, and physical properties such as flexural stiffness,
surface hardness, thermal conductivity, dielectric constant,
abrasion resistance, optical transmissivity, permeability, chemical
stability, bond strength, and other properties. Enhancements to
many of these properties has been exhibited by providing a
conformal coating of one or more layers of diamond-like carbon on a
flexible circuit or carrier feature of surface. In some cases, a
layer or layers of diamond-like carbon will be deposited on the
bare polyimide film prior to forming of the circuit. In other
cases, it will be desirable to coat an intermediate layer or layers
of diamond-like carbon between the various circuit forming steps
such as development, etching, and plating, or between each of these
steps. A layer of diamond-like carbon may also be coated onto any
dielectric layer such as the metallic layers. The desired
attributes of the resulting construction dictate the design,
placement, and number of the diamond-like carbon layers. Any
additional layers must also be flexible enough to bend with the
flex circuits to facilitate processing, handling and assembly
without causing cracking or causing damage to the circuit.
Circuits of the invention may comprise diamond-like carbon layers
coated by any of the variety of methods (ion beam, plasma, etc.)
which have been developed to deposit such layers including those
using either solid carbon or hydrocarbon sources. The deposition
method may be batchwise deposition or continuous deposition,
although continuous deposition is preferred for manufacturing
efficiency.
In preferred articles and processes of the invention, diamond-like
carbon layers are deposited using a continuous plasma process
coupled with ion acceleration. In general, the carbon rich plasma
is created by applying a high frequency electric field to a carbon
containing environment by powering a rotatable electrode element.
Ions within the carbon rich plasma accelerate toward the electrode,
where they strike a substrate in contact with the rotating
electrode.
The diamond-like carbon (DLC) film deposition is made onto a moving
substrate, and the coating apparatus, by providing an electrode in
contact, at least in part, with the moving substrate. The electrode
becomes negatively biased with respect to the plasma, thereby
accelerating the ions toward the electrode, where they strike the
moving substrate resulting in deposition of diamond-like carbon
thereon. This process provides a thin DLC coating in which flaking
is minimized, and the continuous process allows discriminate
coating of substrates rather than indiscriminate coated of the
entire evacuated chamber, providing improved efficiency, reduced
waste, and the like. The diamond-like carbon coating may be formed
in a variety of widths, with little or no cross web variation in
coating weight or thickness. Details of the processes and apparatus
therefore are taught, infra.
The diamond-like carbon may also be surface functionalized with
such materials as fluorine, silicon, oxygen, sulfur, nitrogen,
copper, chromium, titanium, and nickel. Surface functionalization
can be achieved using a blend of suitable gases during the final
stages of diamond-like carbon deposition, by gradually increasing
the respective gas concentration and decreasing the hydrocarbon
precursor concentration. Such process is also called "doping".
When the deposition is done in a continuous mode, as by the
preferred method, the surface functionalization can be accomplished
by installing a box containing the desired alternate gases before
the diamond-like carbon coated web leaves the coating zone.
Suitable silicon gases include, but are not limited to silane
SiH.sub.4, tetramethylsilane (TMS), and tetraethoxysilane (TEOS).
Suitable oxygen gases include but are not limited to oxygen, water
vapor, hydrogen peroxide vapor, ozone, SO.sub.2, and SO.sub.3
Suitable sulfur gases include but are not limited to H.sub.2 S,
SO.sub.2, SO.sub.3, SF.sub.6, carbon disulfide CS.sub.2. Suitable
nitrogen gases include but are not limited to NH.sub.3, NF.sub.3,
NO.sub.2, and N.sub.2 O. Suitable gases using copper include, but
are not limited to, copper acetylacetonate and copper chloride.
Suitable chromium gases include, but are not limited to,
dimethylchromium. Suitable titanium gases include, but are not
limited to, TiCl.sub.3, and TiCl.sub.4. Suitable nickel gases
include, but are not limited to nickel acetate and nickel chloride.
Most can also be co-evaporated or sputtered from their elemental
forms during the final stages of DLC deposition.
The substrate is a flexible polymeric film material which is
substantially fully cured. Useful organic polymers include
polyimides including modified polyimides such as polyester imides
and poly-imide-esters, polysiloxane imides, and polyamide,
polymethylmethacrylate, polyesters such as poly(ethylene
terephthalate), polycarbonates, polytetrafluoroethylenes and
mixtures thereof. The polyimides are preferred, with an especially
preferred polyimide polymer being made from the anhydride of
pyromellitic acid and 4,4 diamino-diphenyl ether available from
E.I. DuPont de Nemours and Company under the tradename Kapton.RTM..
Variations include Kapton.RTM. H, Kapton.RTM. E and Kapton V.RTM.,
among others. Another polyimide precursor is also available from
DuPont as Pyralin.RTM..
The conductive layer(s) are typically formed from conductive metals
such as tin, gold, silver, copper, chromium and the like. The
thickness and disposition of such layers is highly dependent on the
particular type of circuit or electronic package desired.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a flexible circuit carrier 1 having a polymeric
dielectric layer 2 with a layer of diamond-like carbon 4 deposited
between the polymeric dielectric layer 2 and a conductive trace
layer 3. The layer of diamond-like carbon includes a functionalized
region 6 adjacent conductive trace layer 3 for enhancing the bond
strength between the layer of
diamond-like carbon and conductive trace layer 3. The conductive
trace layer 3 includes a seed layer 8 of conductive material and an
electroplated layer 10 of conductive material. The seed layer 8 can
be deposited using techniques such as sputtering, vapor deposition,
vacuum deposition, or other known methods for depositing thin
layers of conductive materials. FIG. 2 shows the same carrier 1 as
shown in FIG. 1 with a layer of diamond-like carbon 4 deposited on
the non-circuit side of the carrier 1. FIG. 3 shows a carrier 1 for
a flexible circuit having a layer of diamond-like carbon 4
deposited on the non-circuit side of the carrier 1. Intermediate
layer 12 is provided to promote adhesion between the dielectric
material 2 and seed layer 8.
FIG. 4 shows a flexible circuit carrier 5 having a layer of
diamond-like carbon 4 over at least portions of the conductive
traces 11. Optionally, the circuit 5 can also have a layer of
diamond-like carbon 4 on the non-circuit side of the polymeric
dielectric layer 2. Intermediate layer 12 is provided to promote
adhesion between the dielectric material 2 and the conductive trace
layer 3.
FIGS. 5 to 7 each show a flexible circuit carrier 1 having a layer
of laser light absorbing material 14 incorporated therein. FIG. 5
shows a carrier 1 with a layer of diamond-like carbon 4 having a
functionalized region 6 deposited on the circuit side of polymeric
dielectric layer 2 and a layer of laser light material 14 deposited
between the diamond-like carbon 4 and the conductive trace layer 3.
In all cases where a layer of metallic material has an interface
with a layer of diamond-like carbon 4, it is preferable for the
layer of diamond-like carbon 4 to have a functionalized region 6 at
the interface. FIG. 6 shows a carrier 1 with laser light absorbing
material 14 deposited on the circuit side of the polymeric
dielectric layer 2 and a layer of diamond-like carbon 4 having
functionalized regions 6 between the laser light absorbing material
14 and the conductive trace layer 3. FIG. 7 shows a carrier 1 with
a layer of diamond-like carbon 4 deposited on the non-circuit side
of polymeric dielectric layer 2. A layer of laser light absorbing
material 14 is deposited on the opposing side of the polymeric
dielectric layer 2 between the polymeric dielectric layer 2 and the
conductive trace layer 3.
FIGS. 8 and 9 each show a flexible circuit carrier 5 having a layer
of laser light absorbing material 14 incorporated therein and at
least one aperture 16 through at least the polymeric dielectric
layer 2 forming cavity 18. The flexible circuit of FIG. 8 includes
intermediate layer 12 for enhancing the bond strength between the
polymeric dielectric layer 2 and the conductive trace layer 3.
Preferably, the aperture 16 of FIG. 8 extends through the polymeric
dielectric layer 2 and through the intermediate layer 12.
Optionally, it could extend only through the dielectric material 2.
A layer of diamond-like carbon 4 is deposited on the non-circuit
side of the polymeric dielectric layer 2 and onto the interior
surfaces 17 of cavity 18. The flexible circuit 5 of FIG. 9 has a
laser light absorbing material 14 deposited on the circuit side of
the polymeric dielectric layer 2 between the dielectric material 2
and the conductive trace layer 3. In FIG. 9, the laser light
absorbing material 14 also serves to enhance the bond strength
between the dielectric material 2 and the conductive trace layer
3.
Each flexible circuit carrier 1 shown in FIGS. 1, 2, 3, 5, 6, and 7
can be used for fabricating 1-metal layer or 2-metal layer
circuits. As shown, each carrier 1 has a conductive trace layer 3
on only one side of the carrier 1. In the case of a 1-metal layer
circuit, the other side of the polymeric dielectric layer 2 would
not have a conductive trace layer 3 formed on it during subsequent
processing steps. In the case of a 2-metal layer circuit, the other
side of polymeric dielectric layer 2 would have a conductive trace
layer 3 formed on it following fabrication of circuit traces on the
first side. In most cases, at least one of the conductive traces on
the first side would be connected to the conductive trace layer on
the second side with one or more metallized vias. One or more
diamond-like carbon layers may also be deposited onto the substrate
layer, sputtered metal layers, electroplated metal layers,
intermediate layers, other dielectric layers, and individual
features of such layers, i.e. bumps or vias.
Description of the Deposition Process
The process of the present invention differs from conventional
carbon coating processes and apparatuses where plasma creation and
ion acceleration are caused by power applied to different elements
and where formation of carbon-rich coatings occur on both the
substrate and the apparatus rather than essentially just the
substrate.
Referring to FIGS. 10 and 11, an embodiment of the carbon film
deposition apparatus of the present invention with a common element
for plasma creation and ion acceleration is generally indicated as
110. This deposition apparatus 110 includes a support structure
112, a housing 114 including a front panel 116 of one or more doors
118, side walls 120 and a back plate 122 defining an inner chamber
124 therein divided into one or more compartments, a drum 126
rotatably affixed within the chamber, a plurality of reel
mechanisms rotatably affixed within the chamber and referred to
generally as 128, drive mechanism 137 for rotatably driving drum
126, idler rollers 132 rotatably affixed within the chamber, and
vacuum pump 134 fluidly connected to the chamber.
Support structure 112 is any means known in the art for supporting
housing 114 in a desired configuration, a vertically upright manner
in the present case. As shown in FIGS. 10 and 11 housing 114 can be
a two-part housing as described below in more detail. In this
embodiment, support structure 112 includes cross supports 140
attached to each side of the two-part housing for supporting
apparatus 110. Specifically, cross supports 140 include both wheels
142 and adjustable feet 144 for moving and supporting,
respectively, apparatus 110. In the embodiment shown in FIGS. 10
and 11, cross supports 140 are attached to each side housing 114
through attachment supports 146. Specifically, cross supports 140
are connected to one of side walls 120, namely the bottom side
wall, via attachment supports 146, while cross supports 140 on the
other side of housing 114 are connected to back plate 122 by
attachment supports 146. An additional crossbar 147 is supplied
between cross supports 140 on the right-hand side of apparatus 110
as shown in FIG. 10. This can provide additional structural
reinforcement.
Housing 114 can be any means of providing a controlled environment
that is capable of evacuation, containment of gas introduced after
evacuation, plasma creation from the gas, ion acceleration, and
film deposition. In the embodiment shown in FIGS. 10 and 11,
housing 114 has outer walls that include front panel 116, four side
walls 120, and a back plate 122. The outer walls define a box with
a hollow interior, denoted as chamber 124. Side walls 120 and back
plate 122 are fastened together, in any manner known in the art, to
rigidly secure side walls 120 and back plate 122 to one another in
a manner sufficient to allow for evacuation of chamber 124,
containment of a fluid for plasma creation, plasma creation, ion
acceleration, and film deposition. Front panel 116 is not fixedly
secured so as to provide access to chamber 124 to load and unload
substrate materials and to perform maintenance. Front panel 116 is
divided into two plates connected via hinges 150 (or an equivalent
connection means) to one of side walls 120 to define a pair of
doors 118. These doors seal to the edge of side walls 120,
preferably through the use of a vacuum seal (e.g., an O-ring).
Locking mechanisms 152 selectively secure doors 118 to side walls
120 and can be any mechanism capable of securing doors 118 to walls
120 in a manner allowing for evacuation of chamber 124, storage of
a fluid for plasma creation, plasma creation, ion acceleration, and
film deposition.
In one embodiment, chamber 124 is divided by a divider wall 154
into two compartments 156 and 158. A passage or hole 160 in wall
154 provides for passage of fluids or substrate between
compartments. Alternatively, the chamber can be only one
compartment or three or more compartments.
Housing 114 includes a plurality of view ports 162 with high
pressure, clear polymeric plates 164 sealably covering ports 162 to
allow for viewing of the film deposition process occurring therein.
Housing 114 also includes a plurality of sensor ports 166 in which
various sensors (e.g., temperature, pressure, etc.) can be secured.
Housing 114 further includes inlet ports 168 providing for conduit
connection through which fluid can be introduced into chamber 124
as needed to supply an environment conducive to film deposition.
Housing 114 also includes pump ports 170 and 172 that allow gases
and liquids to be pumped or otherwise evacuated from chamber
124.
Pump 134 is shown suspended from one of sides 120, preferably the
bottom (as shown in FIG. 11). Pump 134 can be, for example, a
turbo-molecular pump fluidly connected to the controlled
environment within housing 114. Other pumps, such as diffusion
pumps or cryopumps, can be used to evacuate lower chamber 158 and
to maintain operating pressure therein. Sliding valve 173 is
positioned along this fluid connection and can selectively
intersect or block fluid communication between pump 134 and the
interior of housing 114. Sliding valve 173 is movable over pump
port 162 so that pump port 162 can be fully open, partially open,
or closed with respect to fluid communication with pump 134.
Drum 126 preferably is a cylindrical electrode 180 with an annular
surface 182 and two planar end surfaces 184. The electrode can be
made of any electrically conductive material and preferably is a
metal such as, for example, aluminum, copper, steel, stainless
steel, silver, chromium or an alloy of any one or more of the
foregoing. Preferably, the electrode is aluminum, because of the
ease of fabrication, low sputter yield, and low costs.
Drum 126 is further constructed to include non-coated, conductive
regions that allow an electric field to permeate outward as well as
non-conductive, insulative regions for preventing electric field
permeation and thus for limiting film coating to the non-insulated
or conductive portions of the electrode. The electrically
non-conductive material typically is an insulator, such as a
polymer (e.g., polytetrafluoroethylene). Various embodiments that
fulfill this electrically non-conductive purpose so as to provide
only a small channel, typically the width of the substrate to be
coated, as a conductive area can be envisioned by one of ordinary
skill in the art.
FIG. 10 shows an embodiment of drum 126 where annular surface 182
and end surfaces 184 of drum 126 are coated with an electrically
non-conductive or insulative material, except for annular channel
190 in annular surface 182 which remains uncoated and thus
electrically conductive. In addition, a pair of dark space shields
186 and 188 cover the insulative material on annular surface 182,
and in some embodiments cover end surfaces 184. The insulative
material limits the surface area of the electrode along which
plasma creation and negative biasing may occur. However, since the
insulative materials sometimes can become fouled by the ion
bombardment, dark space shields 186 and 188 can cover part or all
of the insulated material. These dark space shields may be made
from a metal such as aluminum but do not act as conductive agents
because they are separated from the electrode by means of an
insulating material (not shown). This allows confinement of the
plasma to the electrode area.
Another embodiment of drum 126 is shown in FIGS. 12 and 13 where
drum 126 includes a pair of insulative rings 185 and 187 affixed to
annular surface 182 of drum 126. In some embodiments, insulative
ring 187 is a cap which acts to also cover end surface 184. Bolts
192 secure support means 194, embodied as a flat plate or strap, to
back plate 122. Bolts 192 and support means 194 can assist in
supporting the various parts of drum 126. The pair of insulative
rings 185 and 187, once affixed to annular surface 182, define an
exposed electrode portion embodied as channel 190.
In any case, electrode 180 is covered in some manner by an
insulative material in all areas except where the substrate
contacts the electrode. This defines an exposed electrode portion
that can be in intimate contact with the substrate. The remainder
of the electrode is covered by an insulative material. When the
electrode is powered and the electrode becomes negatively biased
with respect to the resultant plasma, this relatively thick
insulative material prevents carbon film deposition on the surfaces
it covers. As a result, deposition is limited to the uncovered area
(i.e., that which is not covered with insulative material, channel
190), which preferably is covered by relatively thin substrate
material.
Referring to FIGS. 10 and 11, drum 126 is rotatably affixed to back
plate 122 through a ferrofluidic feedthrough and rotary union 138
(or an equivalent mechanism) affixed within a hole in back plate
122. The ferrofluidic feedthrough and rotary union provide separate
fluid and electrical connection from a standard coolant fluid
conduit and electrical wire to hollow coolant passages and the
conductive electrode, respectively, of rotatable drum 126 during
rotation while retaining a vacuum seal. The rotary union also
supplies the necessary force to rotate the drum during film
deposition, which force is supplied from any drive means such as a
brushless DC servo motor. However, connection of drum 126 to back
plate 122 and the conduit and wire may be performed by any means
capable of supplying such a connection and is not limited to a
ferrofluidic feedthrough and a rotary union. One example of such a
ferrofluidic feedthrough and rotary union is a two-inch (about 5
cm) inner diameter hollow shaft feedthrough made by Ferrofluidics
Co. (Nashua, N.H.).
Drum 126 is rotatably driven by drive assembly 137, which can be
any mechanical and/or electrical system capable of translating
rotational motion to drum 126. In the embodiment shown in FIG. 11,
drive assembly 137 includes motor 133 with a drive shaft
terminating in drive pulley 131 that is mechanically connected to a
driven pulley 139 rigidly connected to drum 126. Belt 135 (or
equivalent structure) translates rotational motion from drive
pulley 131 to driven pulley 139.
The plurality of reel mechanisms 128 are rotatably affixed to back
plate 122. The plurality of reel mechanisms 128 includes a
substrate reel mechanism with a pair of substrate spools 128A and
128B, and, in some embodiments, also can include a spacing web reel
mechanism with a pair of spacing web spools 128C and 128D, and
masking web reel mechanism with a pair of masking web spools 128E
and 128F, where each pair includes one delivery and one take-up
spool. As is apparent from FIG. 11, at least each take-up reel
128B, 128D, and 128F includes a drive mechanism 127 mechanically
connected thereto such as a standard motor as described below for
supplying a rotational force that selectively rotates the reel as
needed during deposition. In addition, each delivery reel 128A,
128C, and 128E in select embodiments includes a tensioner for
supplying tautness to the webs and/or a drive mechanism 129.
Each reel mechanism includes a delivery and a take-up spool which
may be in the same or a different compartment from each other,
which in turn may or may not be the same compartment the electrode
is in. Each spool is of a standard construction with an axial rod
and a rim radially extending from each end defining a groove in
which an elongated member, in this case a substrate or web, is
wrapped or wound. Each spool is securably affixed to a rotatable
stem sealably extending through back plate 122. In the case of
spools to be driven, the stem is mechanically connected to a motor
127 (e.g., a brushless DC servo motor). In the case of non-driven
spools, the spool is merely coupled in a rotatable manner through a
coupling 129 to back plate 122 and may include a tension mechanism
to prevent slack.
A preferred type of substrate is a flexible web. Common examples
include polymeric (e.g., polyester, polyamide, polyimide,
polycarbonate, polyurethane, or polyolefin) webs and webs having at
least one surface including a metallized coating, that can be used
to define one or more electrical circuits. (See, e.g., U.S. Pat.
No. 5,227,008, incorporated herein by reference, for a description
of such a membrane.) When a spool of the latter type of web is
used, the process and apparatus of the present invention can apply
a carbon-rich coating (e.g., a DLC coating) to one surface of the
entire length of the web. Thus, the web or any material coated
thereon, such as an electrical circuit, can be protected by a
uniform coating of a carbon-rich material.
Film deposition apparatus 110 also includes idler rollers 132
rotatably affixed within the chamber and pump 134 fluidly connected
to the chamber. The idler rollers guide the substrate from the
deposition substrate spool 128A to channel 190 on drum 126 and from
channel 190 to take-up substrate spool 128B. In addition, where
spacing webs and masking webs are used, idler rollers 132 guide
these webs and the substrate from deposition substrate spool 128A
and deposition masking web spool 128E to channel 190 and from
channel 190 to take-up substrate spool 128B and take-up masking web
spool 128F, respectively.
Film deposition apparatus 110 further includes a temperature
control system for supplying temperature controlling fluid to
electrode 180 via ferrofluidic feedthrough 138. The temperature
control system may be provided on apparatus 110 or alternatively
may be provided from a separate system and pumped to apparatus 110
via conduits so long as the temperature control fluid is in fluid
connection with passages within electrode 180. The temperature
control system may heat or cool electrode 180 as is needed to
supply an electrode of the proper temperature for film deposition.
In a preferred embodiment, the temperature control system is a
coolant system using a coolant such as, for example, water,
ethylene glycol, chlorofluorocarbons, hydrofluoroethers, and
liquefied gases (e.g., liquid nitrogen).
Film deposition apparatus 110 also includes an evacuation pump
fluidly connected to evacuation port(s) 170. This pump may be any
vacuum pump, such as a Roots.TM. blower, a turbo molecular pump, a
diffusion pump, or a cryopump capable of evacuating the chamber. In
addition, this pump may be assisted or backed up by a mechanical
pump. This evacuation pump may be provided on apparatus 110 or
alternatively may be provided as a separate system and fluidly
connected to the chamber.
Film deposition apparatus 110 also includes a fluid feeder,
preferably in the form of a mass flow controller that regulates the
fluid used to create the thin film, the fluid being pumped into the
chamber after evacuation thereof. The feeder may be provided on
apparatus 110 or alternatively may be provided as a separate system
and fluidly connected to the chamber. The feeder supplies fluid in
the proper volumetric rate or mass flow rate to the chamber during
deposition. In a preferred embodiment, the film created is a thin
carbon film having diamond-like properties. This film is created
from a gas, supplied by the feeder, that contains molecules that
include carbon atoms. Hydrocarbons are particularly preferred,
although such species as buckminsterfullerenes, cyanide,
tetramethylsilane, and halogenated carbon-containing gases such as
fluorocarbons, chlorocarbons, and chlorofluorocarbons also are
potentially useful. Hydrocarbons particularly useful for rapid
carbon-rich (DLC) coatings include benzene, methylcyclopentadiene,
butadiene, pentadiene, styrene, naphthalene, and azulene. Gases
with low ionization potentials, that is 10 eV or less, can be used
and preferably are used for continuous deposition of carbon-rich
coating in this process.
Film deposition apparatus 110 also includes a power source
electrically connected to electrode 180 via electrical terminal
130. The power source may be provided on apparatus 110 or
alternatively may be provided on a separate system and electrically
connected to the electrode via electrical terminal (as shown in
FIG. 11). In any case, the power source is any power generation or
transmission system capable of supplying sufficient power.
Although a variety of power sources are possible, radio frequency
(RF) power is preferred. This is because the frequency is high
enough to form a self bias on an appropriately configured powered
electrode but not high enough to create standing waves in the
resulting plasma, which would be inefficient for ion deposition. RF
power is scalable for high coating output (wide webs or substrates,
rapid web speed). When RF power is used, the negative bias on the
electrode is a negative self bias, i.e., no separate power source
need be used to induce the negative bias on the electrode. Because
RF power is preferred, the remainder of this discussion will focus
exclusively thereon.
The RF power source powers electrode 180 with a frequency in the
range of 0.01 to 50 MHz, preferably 13.56 MHz or any whole number
(e.g., 1, 2, or 3) multiple thereof. This RF power as supplied to
electrode 180 creates a carbon rich plasma from the hydrocarbon gas
within the chamber. The RF power source can be an RF generator such
as a 13.56 MHz oscillator connected to the electrode via a network
that acts to match the impedance of the power supply with that of
the transmission line (which is usually 50 ohms resistive) so as to
effectively transmit RF power through a coaxial transmission
line.
Upon application of RF power to the electrode, the plasma is
established. In an RF plasma the powered electrode becomes
negatively biased relative to the plasma. This bias is generally in
the range of 500 to 1400 volts . This biasing causes ions within
the carbon-rich plasma to accelerate toward electrode 180.
Accelerating ions form the carbon-rich coating on the substrate in
contact with electrode 180 as is described in more detail
below.
In operation, a full spool of substrate upon which deposition is
desired is inserted over the stem as spool 128A. Access to these
spools is provided through lower door 118 since, in FIGS. 10 and
11, the spools are located in lower compartment 158 while
deposition occurs in upper compartment 156. In addition, an empty
spool is fastened opposite the substrate holding spool as spool
128B so as to function as the take-up spool after deposition has
occurred on the substrate.
If a spacer web is desired to cushion the substrate during winding
or unwinding, spacer web delivery and/or take-up spool can be
provided as spools 128C and 128D (although the location of the
spools in the particular locations shown in the figures is not
critical). Similarly, if film deposition is desired in a pattern or
otherwise partial manner, a masking web can be positioned on an
input spool as spool 128E and an empty spool is positioned as a
take-up spool as spool 128F.
After all of the spools with and without substrates or webs are
positioned, the substrate on which deposition is to occur (and any
masking web to travel therewith around the electrode) are woven or
otherwise pulled through the system to the take-up reels. Spacer
webs generally are not woven through the system and instead
separate from the substrate just before this step and/or are
provided just after this step. The substrate is specifically
wrapped around electrode 180 in channel 190 thereby covering the
exposed electrode portion. The substrate is sufficiently taut to
remain in contact with the electrode and to move with the electrode
as the electrode rotates so a length of substrate is always in
contact with the electrode for deposition. This allows the
substrate to be coated in a continuous process from one end of a
roll to the other. The substrate is in position for film deposition
and lower door 118 is sealed closed.
Chamber 124 is evacuated to remove all air and other impurities.
Once a carbon-containing fluid, preferably a gas, is pumped into
the evacuated chamber, the apparatus is ready to begin the process
of film deposition.
The RF power source is activated to provide an RF electric field to
electrode 180. This RF electric field causes the carbon-containing
material to become ionized, resulting in the formation of a carbon
rich plasma with ions therein. This is specifically produced using
a 13.56 MHz oscillator, although other RF sources and frequency
ranges may be used.
Once the plasma has been created, a negative DC bias voltage is
created on electrode 180 by continuing to power the electrode with
RF power. This bias causes ions to accelerate toward non-insulated
electrode portion 190 of electrode 180 (the remainder of the
electrode is either insulated or shielded). The ions bombard the
length of substrate in contact with channel 190 of electrode 180
causing a densification of carbon resulting in the deposition of a
thin diamond-like carbon film on that length of substrate.
For continuous deposition, the take-up spools are driven so as to
pull the substrate and any masking webs through the upper
compartment 154 and over electrode 180 so that deposition occurs on
any unmasked substrate portions in contact with annular channel 190
(otherwise, the masking web receives the carbon film). The
substrate is thus pulled through the upper compartment continuously
while a continuous RF field is placed on the electrode and
sufficient carbon-containing gas is present within the chamber. The
result is a continuous carbon-rich coating on an elongated
substrate, and substantially only on the substrate. Carbon film
deposition does not occur on the insulated portions of the
electrode nor does deposition occur elsewhere in the chamber,
because only the electrode is biased. In addition, since the
non-insulated portion of the electrode (i.e., annular channel 190)
is covered almost or entirely by the substrate, little or no
deposition occurs anywhere but on the substrate. This eliminates
the need for frequent cleaning of the chamber and parts thereof and
replacing the electrode due to carbon buildup. In cases where
fouling of the insulated portion occurs, dark space shields 186 and
188 can be provided to prohibit or reduce fouling. Dark space
shields 186 and 188 can be of any shape, size, and material that is
conducive to the reduction of potential fouling. In the embodiment
shown in FIGS. 10 and 11, dark space shields 186 and 188 are metal
rings that fit over drum 126 and the insulation thereon. Dark space
shields 186 and 188 do not bias due to the insulative material that
covers drum 126 in the areas where dark space shields 186 and 188
contact drum 126. The dark space shields in this ring-like
embodiment further include tabs on each end thereof extending away
from drum 126 in a non-annular manner. These tabs can assist in
aligning the substrate within channel 190.
Preferably, the temperature control system pumps fluid through
electrode 180 throughout the process to keep the electrode at a
desired temperature. Typically, this involves cooling the electrode
with a coolant as described above, although heating in some cases
may be desirable. In addition, since the substrate is in direct
contact with the electrode, heat transfer from the plasma to the
substrate is managed through this cooling system, thereby allowing
the coating of temperature sensitive films such as
polyethyleneterephthalate, polyethylene naphthalate, and the
like.
After completion of the deposition process, the spools can be
removed from shafts supporting them on the wall. The substrate with
a carbon-rich film thereon is on spool 128B and is ready for use
wherever thin carbon film coatings are used, such as for electrical
isolation for chip cooling, flex-metal circuitry, fiber optics,
optical coatings, photo- and microlithographic masks, recording
heads and media, printer heads, orthodontia, abrasives, orthopedic
implants, thin film capacitors, packaging films, laser device
mounts, and numerous other uses.
Low ionization potential gases can be used to obtain extremely high
deposition rates while still maintaining good properties in the
thin carbon film. By using low ionization potential gases, very
fast deposition is possible and low DLC coating film stress is
produced. The DLC coating film stress is 0.4 GPa or lower, in
comparison to 1 to 10 GPa for the DLC film stress reported in
previous DLC coatings. Mass deposition on the substrate is at rates
up to forty or more times higher than the prior art rates of
deposition. Minimal deposition occurs anywhere except on the
substrate, and, as a result, minimal flaking occurs. Furthermore,
deposition is almost entirely due to ion bombardment rather than a
mixture of ion bombardment and free radical contact. In addition,
very high conversion yields (as much as 35%) of gas input to film
output, in comparison to typically single digit yields in the prior
art, can be obtained.
Other benefits and advantages of this process include the ability
to coat over a broader range of substrate dimensions including
widths of from about 15 cm to more than one meter. Substrate width
is not a limiting factor since ion bombardment comes from all
around the substrate in the chamber rather than from a source
specific area. According to the method of the present invention, a
substrate can be coated to a thickness up to about 0.2 .mu.m at a
rate of approximately 1.5 to 6 m/min, generally without regard to
substrate width. Coating thicknesses in the range of 0.1 to 0.3
.mu.m can be produced easily using this process, although thicker
(i.e., up to about 10 .mu.m) and thinner coatings also are
possible.
Overall, plasma generation and ion acceleration is greatly
simplified. Only one electrode is used rather than a source
electrode and a target electrode. The powered electrode both
creates the plasma and becomes negatively biased, thereby
accelerating ions within the plasma toward itself for bombardment
of the substrate in contact with itself. This DC biasing voltage
also serves to density the deposited coating, which enhances the
DLC properties.
Description of the Carrier and Circuit-Making Process
The process of making flexible circuits and carriers according to
the invention comprises the step of depositing at least one layer
of diamond-like carbon thereon which may be used in conjunction
with various known procedures such as metal sputtering, plating
resist laminating, resist exposing, developing, etching, and
plating. The sequence of such procedures may be varied as desired
for the particular application. Multiple deposition steps may be
used where more than one layer of diamond-like carbon is desirable,
e.g., a layer deposited directly on the substrate for improved
planarity and via creation, and a layer deposited atop a metallic
layer to provide such benefits as abrasion resistance and thermal
management. The procedures described herein apply equally to
carriers and flexible circuits.
One additive method for making a flexible circuit or carrier has a
typical sequence of steps described as follows:
First, deposition of a conformal diamond-like carbon layer onto the
polymer, e.g., polyimide side, of a film substrate. The substrate
may be made by various methods such as adhesively bonding a cured
polymer layer onto copper foil, coating liquid polyimide on copper
foil or the like. Typically, the substrate consists of a polymeric
film layer of from about 25 micrometers to about 125 micrometers,
with the copper layer being from about 1 to about 5 micrometers
thick.
Next, sputtering of the polyimide film with a seed layer of chrome
and copper is performed. Photoresists, which may be aqueous or
solvent based, and may be negative or positive photoresists, are
then laminated onto both sides of a substrate having a polymeric
film side and a copper side, using standard laminating techniques
with hot rollers. The thickness of the photoresist is from about 35
to about 50 micrometers. The photoresist is then exposed on both
sides to ultraviolet light or the like, through a mask or
phototool, crosslinking the exposed portions of the resist. The
unexposed portions of the photoresist are then developed with the
appropriate, solvent, in the case of aqueous resists a dilute
aqueous solution, e.g., a 0.5-1.5% sodium or potassium carbonate
solution, is applied until desired patterns are obtained on both
sides of the laminate. The copper side of the laminate is then
further plated to desired circuit thickness. One or more layers of
diamond-like carbon may also be deposited atop the copper if
desired.
The diamond-like carbon layer in the developed area on the other
side is then etched using oxygen plasma to expose the polyimide
surface.
The laminate is then placed into a bath of concentrated base at a
temperature of from about 50.degree. C. to about 120.degree. C.
which etches the portions of the polymeric film not covered by the
crosslinked resist. This exposes certain areas of the original thin
copper layer. The resist is then stripped off both sides of the
laminate in a 2-5% solution of an alkaline metal hydroxide at from
about 20.degree. C. to about 80.degree. C., preferably from about
20.degree. C. to about 60.degree. C. Subsequently, the original
thin copper layer is etched where exposed with an etchant which
does not harm the polymeric film, e.g., Perma-etch.RTM., available
from Electrochemicals, Inc. The final circuits have copper
circuitry on one side, and diamond-like coating on polyimide
surface on the opposing side, and any diamond-like carbon layers
deposited between internal layers or on individual features.
Next come converting and auditing steps where the substrate is cut
into smaller strips.
In an alternate additive process which is preferable where very
hard diamond-like carbon coatings are used, and there is a
propensity for
cracking during early lamination and sputtering steps, the
diamond-like carbon may be deposited on the polyimide side of the
substrate after the flash copper plating step, with the remaining
steps of the process being as described above.
In an alternate type of process called a substractive process,
polyimide film is sputtered with a seed layer of chrome and copper.
The aqueous processible photoresists are laminated onto both sides
of a substrate having a polymeric film side and a thick copper
side, using standard laminating techniques. The substrate used in
this process consists of a polymeric film layer about 12
micrometers to about 125 micrometers thick with the copper layer
being from about 12 to about 40 micrometers thick (in the additive
process, the copper layer is 1-5 micrometers thick).
The photoresist is then exposed on both sides to ultraviolet light
or the like, through a suitable mask, crosslinking the exposed
portions of the resist. The image is then developed with a dilute
aqueous solution until desired patterns are obtained on both sides
of the laminate. The thick copper layer is then etched to obtain
circuitry, and portions of the polymeric layer thus exposed.
The diamond-like carbon is then etched using oxygen plasma or other
comparable processes to expose the polyimide surface.
An additional layer of aqueous photoresist is then laminated over
the first resist on the copper side and crosslinked by flood
exposure to a radiation source in order to protect exposed
polymeric film surface (on the copper side) from further etching.
Areas of the polymeric film (on the film side) not covered by the
crosslinked resist are then etched with the concentrated base at a
temperature of from about 70.degree. C. to about 120.degree. C.,
and the photoresists are then stripped from both sides with a
dilute basic solution. Next come converting and auditing steps.
As with the additive process, the diamond-like carbon layer may be
coated after initial laminating and sputtering steps are completed,
with other processes remaining the steps.
The previous methods coat the conformal diamond-like carbon layer
over the entire substrate. In the selective coating processes, the
layer is coated only in areas of the polyimide surface where
protection is desired. These processes are typically completed
postcircuitization. One selective process is a mechanical masking
process wherein the diamond-like carbon layer is coated through an
appropriate mask after flash etching and converting step.
Other steps may also be included in these processes, such as
soaking the film in hot water before or after the etching bath,
rinse steps and the like. Acid baths may also be used as a
post-etching neutralization, web cleaning steps may follow plating
steps.
To create finished flexible circuits, interconnect bonding tape for
"TAB" (tape automated bonding) processes, microflex circuits, and
the like, further layers may be added and processed, the copper
plating may be plated with gold, tin, or nickel for subsequent
soldering procedures and the like according to conventional means.
When using a selective coating process such as the mechanical
masking process, the diamond-like carbon layer may also be coated
after this final plating step.
Means for interconnection of the flexible circuit to the printed
circuit board or other device may be selected from any conventional
means, connecting the pads or other connection points including
solder balls, reflow solder, thermal compression bonding, wire
bonding, inner lead bonding and the like.
Flexible circuits formed from carriers and processes of the
invention are useful in electronic packages such as ball grid
arrays, chip scale packages, single and multiple metal layer
packages and the like. Such circuits and packages can be designed
for use in any electronic device, including but not limited to
recording devices, printing devices, single or multimedia devices,
projectors, cameras, computers, data storage devices and the
like.
The following examples are meant to be illustrative and are not
intended to limit the scope of the invention which is expressed
solely by the claims.
EXAMPLES
Example 1
Diamond-like carbon films were continuously deposited on a 50
micron Kapton .RTM. web by the process described herein. In this
process, the polyimide web was wrapped around a chilled drum (15.24
cm diameter.times.15.24 cm long) to which radio frequency (rf)
power (at 13.56 Mhz frequency) was supplied. The rf power serves ti
initiate and sustain a plasma of a hydrocarbon gas (butadiene)
utilized to deposit diamond-like carbon films at a pressure of
about 10 mTorr. A steady-state DC self-bias voltage appears on the
substrate web wrapped around the drum, the magnitude of which is
about 1000 V. A series of samples was prepared under the following
conditions of deposition:
______________________________________ Butadiene Estimated flow
rate, Pressure, Power, Web Speed, diamond-like sccm motor watts
cm/min carbon thickness ______________________________________ 60
9.5 600 64 1200 180 9.5 600 190.5 1200 60 9.5 1000 64 1200 180 9.5
1000 190.5 1200 60 9.5 600 27 2800 180 9.5 600 82.3 2800 60 9.5
1000 27 2800 180 9.5 1000 82.3 2800 120 9.5 800 75 2000 120 9.5 800
75 2000 120 9.5 800 75 2000 120 9.5 800 75 2000
______________________________________
Deposition of the diamond-like carbon layer under the above
conditions was performed on a single roll of polyimide film.
Approximately 6.1 m of 15.24 cm (6-inch) wide polyimide film was
coated for each of the conditions above. The diamond-like carbon
coated polyimide film was then sputter coated.
Example 2
Diamond-like Carbon on Copper Plated Circuit Web (Selective
Diamond-like Carbon Deposition, Post Circuitization, Pre-Gold
Plating)
Diamond-like carbon films were deposited continuously over a moving
web by the process described above. The web was a 48 mm wide
circuit web having the metal circuit lines. In a
post-circuitization process, depositing the diamond-like carbon
film prior to gold-plating is desirable if there exists an inherent
yield inefficiency in the diamond-like carbon process. Selective
deposition was achieved by first wrapping the circuit web over the
rf-powered drum and subsequently wrapping the drum with a second
web called the masking web. The masking web is a polyester web
containing rectangular holes to permit diamond-like carbon
deposition to occur on the circuit web only in the rectangular
openings. The circuit and masking webs are registered with respect
to each other by the engagement of their sprocket holes with
sprocket teeth located on the rf powered drum. Diamond-like carbon
films were deposited by decomposing trans 2-butene gas with rf
power (from a 13.56 Mhz generator). Prior to deposition, the
circuit web was cleaned in an argon plasma. The process conditions
are as follows:
______________________________________ Argon Plasma Precleaning:
Argon Flow Rate: 110 sccm Pressure: 30 mTorr Power: 500 Watts Web
Speed: 3 m/min Diamond-like Carbon Deposition: trans 2-Butene Flow
Rate: 200 sccm Pressure: 100 mTorr Power: 500 Watts Web Speed: 2.1
m/min ______________________________________
Approximately 82 meters of circuit web was coated in the above run
which produced diamond-like carbon films selectively over a portion
of the circuit within a placement tolerance of 125 microns. The
resulting diamond-like carbon film thickness is estimated to be
1300 Angstroms.
Example 3
Diamond-like Carbon on Gold-Plated Circuit Web (Selective
Diamond-like Carbon Deposition, Post-Circuitization, Post Gold
Plating)
Diamond-like carbon films were deposited on 48 mm wide circuit web
in which copper plating of circuit lines was followed by gold
plating. The diamond-like carbon deposition process was similar to
Example 2. The DLC films were selectively deposited through a
masking film in two steps, argon plasma precleaning followed by
diamond-like carbon deposition as follows:
______________________________________ Argon Plasma Precleaning:
Argon Flow Rate: 110 sccm Pressure: 40 mTorr Power: 500 Watts Web
Speed: 3 m/min Diamond-like carbon Deposition: trans 2-Butene Flow
Rate: 685 sccm Pressure: 107 mTorr Power: 500 Watts Web Speed: 2.4
m/min ______________________________________
Approximately 106 m of circuit web was coated in the above run
which produced diamond-like carbon films selectively over portions
of the circuit with a placement tolerance of 1.5 mm. The resulting
diamond-like carbon film thickness is estimated to be 1100
Angstroms.
* * * * *